Most complex biological and chemical targets require the application of complementary multidimensional analysis tools and methods to compensate for target and matrix interferences. Correct analysis and separation is important to obtain reliable quantitative and qualitative information about a target. In this regards, mass spectrometers have been used extensively as detectors for various separation methods. However, until recently most spectral methods provided fragmentation patterns that were too complicated for quick and efficient analysis. The introduction of atmospheric pressure ionization (API) and matrix assisted laser desorption ionization (MALDI) have improved results substantially. These methods significantly reduce fragmentation patterns and provide high sensitivity for determining the identity of a variety of compounds. Matrix based ionization techniques have been particularly effective regarding peptides, proteins, carbohydrates, oligosaccharides, natural products, cationic drugs, cyclic glucans, taxol, taxol derivatives, metalloproteins, porphyrins, kerogens, polymers and other biological and non-biological compounds.
Accordingly, in the MALDI or AP-MALDI ionization method, the analyte and matrix in solution is applied to a probe or target substrate. As the solvent evaporates, the analyte and matrix co-precipitate out of solution to form a crystal of the analyte in the matrix on the target substrate. The co-precipitate is then irradiated with a short laser pulse inducing the accumulation of a large amount of energy in the co-precipitate through electronic excitation or molecular vibration of matrix molecules. The matrix dissipates the energy by desorption, carrying the analyte into the gaseous phase. During this desorption process, ions are formed by charge transfer between the photo-excited matrix and analyte although the mechanism of the process is not well known.
MALDI ionization is typically performed using a time-of-flight analyzer. Other mass analyzers such as an ion trap, an ion cyclotron resonance mass spectrometer and quadrupole time-of-flight are also used. These spectrometers have a number of problems because they are required to operate under high vacuum. For instance, they limit target throughput, reduce resolution, capture efficiency and make testing targets more difficult and expensive to perform.
To overcome the disadvantages described above, another technique call AP-MALDI has been developed. This technique performs similar ionizations, but at atmospheric pressure. The MALDI and AP-MALDI ionization techniques have much in common. These techniques are based on the process of a pulsed laser beam desorption/ionization of a solid-state target material resulting in production of gas phase analtye molecular ions. The ion plume is produced as a result of ionization from a solid support or plate.
A number of techniques and components have been designed to try to improve the sensitivity of these instruments. For instance, heat or heated gas flow has been introduced into the chamber or ionization region to improve the ionization process. In addition, different type plates have been developed to improve ionization. For instance, various materials have been employed to increase the hydrophobicity of the materials used on the plate surface. Improvements of the surface or surface composition have been useful in improving the overall efficiency of ion plume and ion production. This improves overall instrument performance and signal to noise ratio. For some time improvements in materials and their hydrophobicity have been problematic. These limitations and others have been obviated by the present invention.